libstdc++
omp_loop.h
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24 
25 /** @file parallel/omp_loop.h
26  * @brief Parallelization of embarrassingly parallel execution by
27  * means of an OpenMP for loop.
28  * This file is a GNU parallel extension to the Standard C++ Library.
29  */
30 
31 // Written by Felix Putze.
32 
33 #ifndef _GLIBCXX_PARALLEL_OMP_LOOP_H
34 #define _GLIBCXX_PARALLEL_OMP_LOOP_H 1
35 
36 #include <omp.h>
37 
38 #include <parallel/settings.h>
40 #include <parallel/base.h>
41 
42 namespace __gnu_parallel
43 {
44 /** @brief Embarrassingly parallel algorithm for random access
45  * iterators, using an OpenMP for loop.
46  *
47  * @param begin Begin iterator of element sequence.
48  * @param end End iterator of element sequence.
49  * @param o User-supplied functor (comparator, predicate, adding
50  * functor, etc.).
51  * @param f Functor to "process" an element with op (depends on
52  * desired functionality, e. g. for std::for_each(), ...).
53  * @param r Functor to "add" a single result to the already
54  * processed elements (depends on functionality).
55  * @param base Base value for reduction.
56  * @param output Pointer to position where final result is written to
57  * @param bound Maximum number of elements processed (e. g. for
58  * std::count_n()).
59  * @return User-supplied functor (that may contain a part of the result).
60  */
61 template<typename RandomAccessIterator,
62  typename Op,
63  typename Fu,
64  typename Red,
65  typename Result>
66  Op
67  for_each_template_random_access_omp_loop(RandomAccessIterator begin,
68  RandomAccessIterator end,
69  Op o, Fu& f, Red r, Result base,
70  Result& output,
71  typename std::iterator_traits
72  <RandomAccessIterator>::
73  difference_type bound)
74  {
75  typedef typename
76  std::iterator_traits<RandomAccessIterator>::difference_type
77  difference_type;
78 
79  difference_type length = end - begin;
80  thread_index_t num_threads =
81  __gnu_parallel::min<difference_type>(get_max_threads(), length);
82 
83  Result *thread_results;
84 
85 # pragma omp parallel num_threads(num_threads)
86  {
87 # pragma omp single
88  {
89  num_threads = omp_get_num_threads();
90  thread_results = new Result[num_threads];
91 
92  for (thread_index_t i = 0; i < num_threads; ++i)
93  thread_results[i] = Result();
94  }
95 
96  thread_index_t iam = omp_get_thread_num();
97 
98 # pragma omp for schedule(dynamic, _Settings::get().workstealing_chunk_size)
99  for (difference_type pos = 0; pos < length; ++pos)
100  thread_results[iam] =
101  r(thread_results[iam], f(o, begin+pos));
102  } //parallel
103 
104  for (thread_index_t i = 0; i < num_threads; ++i)
105  output = r(output, thread_results[i]);
106 
107  delete [] thread_results;
108 
109  // Points to last element processed (needed as return value for
110  // some algorithms like transform).
111  f.finish_iterator = begin + length;
112 
113  return o;
114  }
115 
116 } // end namespace
117 
118 #endif /* _GLIBCXX_PARALLEL_OMP_LOOP_H */
Runtime settings and tuning parameters, heuristics to decide whether to use parallelized algorithms...
Op for_each_template_random_access_omp_loop(RandomAccessIterator begin, RandomAccessIterator end, Op o, Fu &f, Red r, Result base, Result &output, typename std::iterator_traits< RandomAccessIterator >::difference_type bound)
Embarrassingly parallel algorithm for random access iterators, using an OpenMP for loop...
Definition: omp_loop.h:67
GNU parallel code for public use.
Sequential helper functions. This file is a GNU parallel extension to the Standard C++ Library...
uint16 thread_index_t
Unsigned integer to index a thread number. The maximum thread number (for each processor) must fit in...
Definition: types.h:141
Includes the original header files concerned with iterators except for stream iterators. This file is a GNU parallel extension to the Standard C++ Library.